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Abstract

The application of ground granulated blast furnace slag (GGBFS) and steel fibers in prestressed concrete railway sleepers was investigated in this study. The use of GGBFS was considered as an eco-friendly material aimed at reducing CO2 emissions and energy consumption as well as to enhance the durability performance of railway sleepers. Steel fibers improves the durability and structural performance in terms of crack control and reduction of spalling and can replace shear reinforcement. The mix proportions of the concrete incorporating GGBFS (56% GGBFS) and GGBFS with steel fibers (56% GGBFS and 0.75% steel fibers) were determined through a series laboratory tests and a life cycle assessment. These mixes satisfied the requirements of the Korean Railway Standard and resulted in improved flexural capacity as well as less CO2 emissions compared with current railway sleepers. Using these mixes, a total of ninety prestressed concrete sleepers were produced in a factory under the same manufacturing process as current railway sleepers, and their mechanical properties as well as durability performance were evaluated. The mix with partial replacement of Type III Portland cement by GGBFS showed an improved resistance to chloride ion penetration and freeze-thaw cycles compared with the concrete used for current railway sleepers. However, these mixes were more vulnerable to carbonation. The mix with GGBFS and steel fibers (mix BSF) showed a slightly better durability performance than the mix with GGBFS only (mix BS), including better carbonation and freeze-thaw resistances. The mix BSF showed decreased chloride ion penetration depth than mix BS but showed a slightly higher chloride ion diffusion coefficient.

5. Conclusions

The use of ground granulated blast furnace slag (GGBFS) and steel fibers for concrete mixes for railway sleepers has been investigated. The appropriate mix proportions, mechanical properties, and durability performance of these mixes were discussed in this study, and following conclusions can be drawn: 1) The mix proportions with partial replacement of Type III Portland cement by ground granulated blast furnace slag were evaluated and mixes with a 56% slag replacement level showed not only improved performance but also less CO2 emissions. 2) The use of 0.75% of steel fibers in a slag concrete mix results in enhanced static and impact flexural capacity and toughness as well as sufficient workability for concrete casting. 3) Using new mixes incorporating GGBFS and GGBFS with steel fibers, a total of ninety prestressed concrete sleepers were produced under the same production process used for conventional railway sleepers. Concrete with the new mixes exceeded the strength requirements of the Korean Railway Standard but the strengths were somewhat lower than the laboratory mix test results. This underlines the need for careful quality control of the concrete for producing prestressed concrete sleepers. 4) The durability performance of the concrete mixes for prestressed concrete sleepers was also evaluated in terms of chloride ion penetration, carbonation, freezing and thawing, and scaling resistance. The mix with GGBFS (partial replacement of Type III Portland cement by GGBFS) showed improved resistance to chloride ion penetration and freeze-thaw cycles compared to the conventional concrete mix currently used for railway sleepers. The mix with GGBFS was more vulnerable to carbonation, however the predicted depth of carbonation was less than the concrete cover after 50 years of service.